Copper-carbon contact



Dec. 16, 1930. s. M. DAY 1,785,618

COPPER CARBON CONTACT Original FiledA r i; 9. 1920 rammed Dec. 16, 1930 UNITED STATES PATENT OFF-ICE SALISBURY 1!. DAY, OF ROCHESTER, NEW YORK, ASSIGNOR TO GENERAL RAILWAY SIGNAL COMPANY, OF ROCHESTER, NEW YORK,- A CORPORATION OF NEW YORK COPPER-CARBON CONTACT Original application filed April 9, 1920, Serial No. 372,585. Divided and this application filed September 22, 1926. Serial No. 137,137.

number of operations.

With the above and other objects in view, the present invention provides contacts satisfying the requirements set forth above.

Further objects, purposes, and characteristic features of this invention will appear as the description progresses, reference being had to the accompanying drawing showing one-embodiment of the invention solely by way of example, and wherein The single figure of drawing is a side elevation with parts shown in section, of contact means in accordance with this invention.

Referring to the drawing, there is shown a movable contact member 52, made, for example of 99.9 fine silver, or other highly conductive, non-corrosive metal, mounted on a carrying spring arm riveted to a contact finger 34 which is carried and actuated in any usual or desired manner.

A front contact member, cooperating with the metal contact 52, is carried by the binding post F, and comprises a stem which is threaded into an axial bore in the binding post F so that this member may be adjusted up and down. A jam nut and washer 56 on this stem 55 engages the bottom of a recess in the under face of the top plate 1, and not only clamps the binding post F in place, but also locks said stem in its adjusted position. The lower end of the stem 55 is provided with a jaw or socket, in which the contact element 57 is fastened by a screw 58. This front contact element 57.is in the form of a rectangular block, with a hole for receiving the screw 58.

In relays for railway signaling, as stated,

the contacts should be non-fusing, have a low contact resistance, with a relatively small contact pressure, and be capable of maintaining such low resistance in service after a large number of operations. To prevent fusing, one of the contact elements is made of some form of carbon, the other element being any suitable highly conductive non-corrosive metal, such as 99.9 per cent fine silver. The use of a carbon contact element, however, gives a relatively high contact resistance, and to reduce this resistance I impregnate or saturate the carbon element with a small percentage of copper. Instead of carbon in the form of graphite, which has the objectionable greasy property causing it to form in time a film or coating on the metal element, increase the contact resistance and make it fluctuate in service, I employ a hard dense carbon, having a crystalline structure. A carbon which I find satisfactory for this purpose in an oil or gas furnace product, which is ground up into a fine flour and then pressed together at high temperature with a suitable binder to give a homogeneous and uniform structure. The constituent parts of this carbon are treated and selected so that the carbon is suflicient- 1y porous to receive a small percentage of pure copper. The percentage of copper may be varied, to suit particular conditions. As larger percentages of copper are used, lower contact resistance is obtained, but the tendency to fuse is increased. I find that from about five to fifteen per cent of copper by volume provides a non-fusing element having the desired low contact resistance; and I find ten per cent of copper, or as nearly ten per cent as can be obtained in commercial manufacture, gives satisfactory results under the average conditions found in practice. The impregnation of the carbon with copper is preferably made by a combined vacuum and pressure process, so that thecopper is as uniformly distributed as possible. This contact element is dense and hard, in fact, so hard that it cannot be worked by ordinary tools but must be finished with carborundum wheels or other hard grinding compound. I

find that such a carbon contact, element gives inpracti'ce a low contact resistance with coin silver of approximately .15 to .25 ohms, with a contact pressure of from approximately 1 to 2- ounces per contact. Moreover, this low contact resistance stays constant in regular service, and will be as low, or perhaps lower, after many operations.

The contact spring 50, carrying the metal contact element, is normally set at an angle with respect to the surface of the carbon element 57 (see Fig. 1), so that when the armature of the relay is attracted, this spring is flexed slightly, and the silver tips 52 are slightly wiped or rubbed over the surface-of said carbon element. 1 This slide cleans the surface of the contact elements, thereby maintaining them in condition to make an intimate and low resistance contact, and also causes the circuit to be broken at a difierent point than where the current is carried normally while the relay is energized. The parts are adjusted in manufacture so that the desired contact pressure and rub are obtained.

The above rather specific description of one form of the present invention is given solely by way of illustration and is not intended in any manner whatsoever in a limiting sense. Obviously this invention can assume many different forms and is susceptible of various modifications, and all such forms and modifications are-contemplated as being included by this invention as come within the scope of the appended claims.

Havmg described one form of the present invention, I now claim 1. In a relay adapted for railway signaling systems, a contact element of a highly conductive non-corrosive metal, and a cooperating contact element of hard dense carbon of a crystalline structure impregnated with approximately ten per cent by volume of pure copper.

2. A contact element for relays capable of maintaining a constant low contact resistance with a metal at relatively small contact pressures, comprising a block of hard dense carbon impregnated with not more than 15 per cent of copper.

3. A contact element for relays, comprising, a block or dense, hard, crystalline car-' -bon impregnated with from to 15 per cent of copper.

4. A contact element for relays, comprising, a block of dense, hard, crystalline carbon, impregnated with approximately 10 per cent of copper.

' 5. In a relay, a contact element of hard carbon impregnated with from 5 to 15 per cent of copper, and a co-o rating contact element of coin silver positioned to wipe across the carbon element when contacting with the same.

In testimony whereof I have aflixed my signature.

SALISBURY M. DAY. 

